Vehicles incorporating tandem drive axles benefit in many ways over vehicles having a single driven axle. Inter-axle differentials in such vehicles may be configured to distribute torque proportionately or disproportionately between the axles. Additionally, shift mechanisms may be provided to such vehicles to permit the disengagement of one of the driven axles or to transition from single axle operation to tandem axle operation, among other benefits.
Such shiftable, multi-mode tandem drive axles have complex shift mechanisms that tend to be expensive. Further, such tandem drive axles may suffer from hardware problems relating to sequencing an engagement of the various components. Two technologies commonly used in such shift mechanisms are electronic and pneumatic sequencing. Tight control of shifting events using these technologies increases cost and fault mode concerns of the tandem drive axle. Substantial hardware problems can occur if shifting events of the tandem drive axle are out of sequence. Tandem drive axles require a shift method that ensures the required operating modes are achieved in a reliable manner with a minimum of complexity.
It would be advantageous to develop a mechanically operated shift assembly for a tandem drive axle system that reduces complexity and a cost of such shift mechanisms while ensuring reliable and safe operation.